Infectious Bursal Disease, also called “Gumboro Disease,” is an acute and highly contagious viral infection of young chickens and other fowl. It is caused by Infectious Bursal Disease Virus (IBDV) Type I, which is a member of a group of viruses called Birnaviridae. The disease is characterized by degeneration of lymphoid tissue. The primary target of infection is the bursa of Fabricius, although lymphoid damage may also occur in the spleen, thymus, and gland of Harder.
Degeneration of the bursa of Fabricius and other lymphoid tissue in young chickens has severe economic consequences, as the infected chickens have a decreased response to vaccination and an increased susceptibility to other infectious agents such as Newcastle disease, Marek's disease and infectious bronchitis disease. Poultry producers can lose a significant portion of their flock due to IBDV infection. Often times, mortality rates can approach 80% or more in young chickens.
Immunization is the principal method for controlling the disease. Chickens may be passively immunized, by receiving maternally-derived antibodies, or they may be actively immunized with live, live-attenuated, or killed (inactivated) vaccines. Live-attenuated vaccines contain the virus that has been “modified” or attenuated through serial passaging in cell culture. By passaging it is hoped to produce a virus strain that is less pathogenic. In order to be useful in a vaccine, however, it must retain the antigenic and immunogenic properties of the original virus. It must, that is, induce the production of neutralizing antibodies. Control of the disease by immunization had been largely successful until variant strains began to emerge as the result of antigenic drift under field conditions. These variants were causing disease in both actively and passively immunized chickens.
Infectious Bursal Disease Virus is often separately classified in the art as either Standard or “STC” strain, or variant types, although the vast majority of wild-type IBDVs in the United States are now variants. Delaware viruses are some of the most common variant types, and Delaware E in particular has been considered the prototypical variant type for years. IBDV surveys indicate that Delaware E virus is still commonly isolated; however, other variant virus types such as GLS, Rs593 and AL2 have also become quite prevalent. These strains can be characterized using a panel of monoclonal antibodies. In addition, using PCR-RFLP techniques, a distinct molecular class of viruses (called Group 6) have risen in prevalence over the past several years. Amino acid sequencing of this family of viruses shows that most are distinct from the prototype Delaware-E virus in the region generally regarded as perhaps one of the most critical to antigenic identity or uniqueness.
U.S. Pat. No. 5,919,461 relates to a live, variant vaccine strain which is reportedly effective in immunizing young chickens against the Standard, the Delaware and other new-type variant strains.
U.S. Pat. No. 6,471,962 discloses the use of certain monoclonal antibodies in the diagnosis, prevention and treatment of Infectious Bursal Disease.
U.S. Pat. No. 5,192,539 relates to an IBDV vaccine for poultry with antigen material which is derived from a mammalian cell line.
U.S. Pat. No. 5,804,195 provides a vaccine for preventing infectious bursal disease which contains specific strains of live, attenuated but intermediately virulent IBDV. The vaccine may contain other poultry immunogens, including those against Newcastle Disease virus, Marek's disease virus, and infectious bronchitis virus.
In addition, WO 9105569 is related to a diagnostic and vaccine which utilizes an IBDV variant with altered recognition sites.
There currently exists a need in the art for better antigenic isolates of IBDV, as well as vaccines which comprise these isolates for use against IBDV infection. Also needed are better methods of protecting poultry, in particular chickens, from the many variants of the IBD virus, including newer ones that have recently emerged.